Valves are used to regulate fluid flow in a wide variety of commercial and industrial applications. For example, valves are used to regulate steam in the pipes of nuclear power plants, water in the pipes of water supply systems, and air in the ducts of air conditioning systems.
Valves are typically controlled manually and/or electronically. Electronically controlled valves often receive command signals through a set of wires. The power needed to run the positioner of a valve may be derived from the command signals or delivered through a separate set of wires.